1. Field of the Invention
This invention relates to an erasable and programable read only memory device, more particularly to an erasable and programable read only memory device (EPROM) contained in a package having a window for injecting light.
2. Description of the Prior Art
In recent years, an erasable and programable read only memory device (EPROM) of the type on which data electrically written and erased by ultraviolet rays is used in many applications, because the content of the memory device can be rewritten as desired by a user. Generally, the IC chip of the prior art EPROM device has been sealed in a dual line type ceramic package.
As shown in FIG. 1, the chip 4 is secured to a metallized surface of the cavity portion 3 of a ceramic substrate by an alloying method. A plurality of lead wires 1 are secured to the surface of the ceramic substrate 2 by using low-melting point glass and the lead wires are mutually connected by an aluminum wire 5 for the purpose of connecting the lead wires to the chip 4.
A ceramic cap 7 having a glass lens 6 for transmitting ultraviolet rays is mounted on the top of the ceramic substrate 2. While maintaining the lens 6 and the chip 4 in an aligned state, the ceramic substrate 2 and the ceramic cap 7 are secured together with the low melting point glass so as to perfectly seal the chip 4.
Such a prior art EPROM device, however, has various defects as follows.
More particularly, the ceramic package provided with a window requires a number of parts so that its manufacturing cost is high.
Furthermore, it has been essential to use low melting point glass for sealing the ceramic package. For providing a seal with low melting glass, the IC chip is heated at a temperature of about 480.degree. C. for more than 5 minutes so that it has been impossible to use gold wires for interconnecting the bonding pads and lead wires made of aluminum of the chip, whereby high speed bonding is difficult, thus increasing the cost of manufacturing.
Moreover, as the specific gravity of the ceramic package and the low melting glass is high, where a large number of EPROM devices are mounted on a printed board of a computer, the weight thereof increases and its handling becomes inconvenient.
Due to these problems, it has been desired to provide a plastic molded EPROM device. However, it is very difficult to provide a light transmitting window for a molded IC package thus failing to realize an EPROM device having high reliability.